The delivery of a package mailed to a tenant of a multiple tenant building, such as an apartment house or office building, or to a person receiving mail at a centralized pickup point in a rural community, such as may be located for use by tenants of a trailer park, has been a time-consuming procedure both for the mailman charged with its delivery and for the intended recipient. In this respect, letter boxes normally provided for tenants of a multiple tenant building or trailer park are not of a size sufficient to receive medium to large size packages, and thus it has been necessary for the mailman to carry such packages directly to the door of the intended recipient. In the absence of the recipient, it is necessary for the mailman to return the package to the Post Office to await its personal pickup by the recipient.
A solution to the foregoing problem is offered by a mailbox unit of the type described in U.S. Pat. No. 3,790,244. In this patented unit, a plurality of large sized package storage cabinets are provided in proximity to a plurality of conventionally sized, key controlled letter boxes permanently assigned one to each tenant. The door of each storage cabinet is provided with a pair of key operated locks, namely, a custodian lock, which is operable by a key continuously retained in the possession of the mailman, and an access or recipient lock, which is over-controlled by the custodian lock for single-shot door opening operation by an access key placed in the temporary custody of an intended recipient of a package.
More specifically, when the mailman wishes to deliver a package, he places the package in one of the storage cabinets and then places its associated access key, which is appropriately numbered or otherwise marked in conformity with such cabinet, in the intended recipient's letter box. The presence of an access key in his letter box automatically advises the intended recipient that he has received a package and he then uses such key to open the door of the appropriate storage cabinet to gain access to his package. As the access key is turned to unlock the access lock in order to permit opening of the storage cabinet door, a latch device controlled by the custodian lock automatically locks the access lock in unlocked condition, with the result that its access key is "captured" or retained in the access lock. During a subsequent mail delivery, the mailman may reuse the now empty storage cabinet by placing another package therein and then employing his key to momentarily unlock the custodian lock in order to release the access lock for return to its cabinet door locked condition. The access key may then be removed and deposited in an appropriate letter box.
While a post office locker having a custodian lock/access lock latching arrangement of the type described in U.S. Pat. No. 3,790,244 is quite effective for security purposes, it has not been placed in wide use, due to the insistence on the part of postal authorities that post office lockers of the general type described in this patent be fitted with an approved or standard custodian lock fitted with a lock housing mounting a reciprocating lock bolt. This requirement has resulted in the adoption in the industry of a decidedly different access lock latching arrangement, wherein a spring latch element, which is supported for rotation with the access lock, is arranged and shaped to resiliently override the lock bolt of the custodian lock, during rotation of the access lock towards door unlocked position and then to latchingly engage with such lock bolt to prevent return rotation of the access lock towards locked position, until operation of the custodian lock for purposes of momentary retraction of the lock bolt. Spring devices have sometimes been employed to normally bias the access lock towards unlocked position.
A drawback to the present industry accepted custodian lock/access lock latching arrangement is that on occasion such arrangement has been found to allow the access lock to be rotated towards its unlocked position sufficiently to permit opening of its associated door for package removal purposes prior to the point at which the spring latch element becomes effective for purposes of cooperation with the lock bolt of the custodian lock to prevent return rotation of the access lock to its locked position, whereat the access key can be removed from the access lock. Thus, on these occasions, it is possible to remove a package and then remove and retain/discard the access key, such that the package storage cabinet is rendered unusable until a new access lock/access key unit is installed. This failure in the present system may occur for various reasons including damage to the door or its surrounding frame, which permits premature separation of the lock bolt of the access lock carried on one of the door or frame from its cooperating locking flange or recess carried on the other of the door or frame. The problem is aggravated by the fact that manufacturers of post office lockers do not have control of the manufacture of the lock units required to be installed and thus it is difficult to accurately control manufacturing tolerances, as required to insure that unlocking of the door occurs only after the key of the access lock has been "captured" by the custodian lock.